Structural bolts are at the heart of steel construction in Australia and New Zealand. Every beam splice, column base and bracing connection relies on bolts to transfer load safely for decades. When these bolts are carefully selected, correctly installed and properly inspected, they quietly do their job and nobody thinks about them again. When something goes wrong, however, bolt problems can lead to connection slippage, serviceability issues or even serious safety concerns.
For overseas buyers, engineers and distributors supplying into AU and NZ, understanding structural bolts is essential. You are not just buying “hex bolts”; you are buying complete assemblies that need to match local standards, construction categories and installation methods. This article explains the main standards, bolt types, coatings, installation requirements and quality control points, with a focus on practical tips for procurement and communication with your fastener supplier.
What makes a bolt “structural” in AU/NZ?
In everyday language people may call any large bolt a structural bolt, but in Australian and New Zealand practice the term usually refers to high-strength bolt assemblies used in steel structures in accordance with AS/NZS 1252 and related standards. These bolts are designed for critical load-bearing connections such as:
- Beam-to-column and beam-to-beam splices
- Column splices and base plates
- Bracing and moment connections
- Connections in bridges, industrial plants and towers
Key characteristics of structural bolt assemblies include:
- High strength alloy or medium-carbon steel
- Specific property classes (commonly 8.8 or 10.9)
- Matching nuts and washers supplied as an assembly, not random loose items steel.org.au
- Controlled dimensions and thread forms
- Traceability and verification testing requirements
These assemblies are quite different from commercial bolts used for general fixing. Using the wrong grade or a non-conforming assembly in a structural joint can greatly reduce its capacity and reliability.
Main standards for structural bolts in AU and NZ
Several key standards govern how structural bolts are manufactured, specified and installed.
AS/NZS 1252 – High-strength bolt assemblies
AS/NZS 1252 (now split into Parts 1 and 2) defines high-strength steel fastener assemblies for structural engineering – bolts, nuts and washers. Part 1 sets technical requirements for assemblies, while Part 2 covers verification testing. steel.org.au+1
Important points from AS/NZS 1252.1 include:
- Bolt property classes and mechanical properties
- Nut and washer requirements compatible with the bolt strength
- Dimensional tolerances and thread forms
- Marking, labelling and traceability of assemblies
For buyers, the key takeaway is that structural bolts, nuts and washers should be ordered and supplied as assemblies certified to AS/NZS 1252, not mixed from unrelated batches.
AS/NZS 5131 – Fabrication and erection of structural steelwork
AS/NZS 5131 is the fabrication and erection standard for structural steelwork. It is now referenced by both Australian and New Zealand authorities as good practice for steel construction. Steel Construction New Zealand+2steel.org.au+2
This standard:
- Defines construction categories (CC1–CC4) based on risk and complexity
- Gives requirements for bolting, including tightening categories and inspection
- Links to AS/NZS 1252 for the bolt assemblies themselves
The higher the construction category, the more stringent the documentation, traceability and inspection expectations are.
AS 4100 and related design standards
AS 4100 (Steel Structures) and associated design guidance describe how structural bolts are used in design calculations, including:
- Shear and tension capacity
- Slip resistance for friction-type joints
- Minimum edge distances and spacing
Design guides from industry organisations summarise the relevant Australian Standards for bolting and explain how high-strength structural bolts to AS/NZS 1252 fit into the overall system. 设计手册+1
Types of structural bolt assemblies
Although each project is unique, some common structural bolt types are widely used across AU and NZ.
Standard high-strength hex bolt assemblies
These are large hexagon head bolts with matching nuts and washers, usually in property class 8.8 or 10.9 and diameters from M16 up to M36 or M39. They are used in:
- Steel building frames
- Bridges
- Industrial structures and conveyors
Typically they are supplied either plain (black) or hot dip galvanized, depending on the corrosion category of the environment. Technical data from suppliers shows that hex bolts designed for structural and heavy-duty applications can be tightened with standard tools while delivering high clamp loads. Jiaxing Linkworld Fastener
You can see typical hex bolt products here:
https://linkworldfast.com/product/hex-bolts/
Structural washers and nuts
Structural bolts must be used with compatible structural nuts and washers. Washers are often thicker and larger in diameter than commercial washers to spread load and protect the steel surface. For example, AS1252 structural washers are specifically used in conjunction with high-strength bolts in structural steel connections. Jiaxing Linkworld Fastener+1
Example product:
https://linkworldfast.com/product/as1252-structural-washer/
Nuts are typically heavy hex style, made from steel with strength and hardness suitable for the bolt grade. The assembly is designed so that, when correctly tightened, the bolt will yield before the nut strips.
Hold-down bolts and anchor rods
In addition to main frame connections, structural bolts are widely used in base plate and hold-down applications. These may be:
- Cast-in anchor rods with nuts and plates
- Chemical stud anchors
- Post-installed heavy-duty anchors
While not always covered by AS/NZS 1252, they are still part of the overall structural bolting system and often specified in conjunction with steelwork design.
Coatings and corrosion protection
Australia and New Zealand have many coastal and industrial environments with high corrosion risk. Choosing suitable coatings for structural bolts is critical.
Common options include:
- Hot dip galvanizing – Very common for external steelwork. Provides a thick zinc coating that protects both bolt and nut. Friction factors must be considered when designing slip-critical joints.
- Mechanical or zinc flake coatings – Used when a thinner, more controlled coating is needed, especially for preloaded friction joints.
- Plain (black) finish – Used in internal dry environments or where other protective measures exist, such as paint systems after erection.
Design guides on Australian bolting standards note that bolt coating and lubrication have a strong influence on torque–tension relationships and slip resistance, and must match the assumptions used in design. 设计手册
When discussing orders with your supplier, always link coating choices to the job’s corrosion category and construction category.
How structural bolts work in different joint types
Structural bolts are used in several joint categories, each with different performance expectations.
Bearing-type (shear) joints
In bearing joints, bolts work primarily in shear, with some bearing between the bolt shank and the hole. Slip between plates is usually acceptable within defined limits. These joints often use snug-tight or fully tensioned bolts, depending on the design.
Tension-type joints
Here, the main load is axial tension in the bolt – for example, in tension braces or flange connections where uplift occurs. Correct preload is essential to maintain clamping force and prevent fatigue or loosening.
Slip-critical (friction-type) joints
In slip-critical joints, movement between plates is not allowed under service loads. The design relies on friction between faying surfaces, generated by high bolt preload. Any loss of preload, incorrect surface treatment or wrong friction classification can reduce capacity.
Australian design guidance explains that high-strength structural bolts to AS/NZS 1252 are suitable for both bearing and friction-type joints, but surface preparation, bolt tension and inspection must align with the design assumptions. 设计手册
Tightening categories and installation methods
AS/NZS 5131 and supporting guides define tightening categories for structural bolting. While terminology may differ between documents, two broad levels are commonly recognised:
- Snug-tight (or bearing) category – Bolts are tightened to bring plates into firm contact using a standard wrench or impact tool, without achieving full pre-tension.
- Fully tensioned (preloaded) category – Bolts are tightened to a specified minimum tension to meet slip-critical or fatigue design requirements.
Several methods are used to achieve and verify full tension:
- Torque method – Applying a calibrated torque using torque wrenches or calibrated impact tools.
- Turn-of-nut method – Tightening to snug-tight, then rotating the nut by a specified angle based on bolt length.
- Direct tension indicators (DTIs) – Using special washer devices that deform at a known load, providing direct evidence of bolt tension.
The new steelwork fabrication standard emphasises that tightening and inspection procedures must match the construction category and project documentation, with higher categories requiring more formal control and record keeping. Steel Construction New Zealand+2steel.org.au+2
For overseas suppliers, it is important to understand which tightening category the customer intends to use. This influences not only bolt grade and coating, but also the need for calibrated assemblies and detailed documentation.
Inspection and quality control for structural bolts
Given their importance, structural bolts are subject to stricter quality and inspection requirements than general fasteners.
Verification testing and documentation
AS/NZS 1252.2 sets out verification testing requirements for bolt assemblies, including:
- Tensile and proof load tests
- Hardness and impact tests
- Coating thickness and adhesion tests
- Torque–tension or wedge tests where relevant steel.org.au+1
Industry fact sheets from steel construction bodies provide practical guidance on how fabricators and importers can verify compliance, especially during the transition to new editions of the standard. Steel Construction New Zealand
As a buyer, you should consider:
- Requesting test reports for each batch or lot
- Checking that the standard and property class on the reports match your order
- Confirming which laboratory carried out the testing
Traceability and marking
High-strength structural bolts, nuts and washers are marked to identify:
- Manufacturer or supplier
- Property class
- Standard reference
Labels on cartons and pallets should clearly show item code, size, grade, coating, batch number and quantity. In higher construction categories, projects may require full traceability from installed bolt back to test reports.
Site inspection
On site, inspectors will check:
- Correct bolt type, grade and coating
- Presence of required washers (for example, under the turned element)
- Tightening method used and any torque records
- Evidence of full tension where required (e.g. flattened DTI bumps)
If bolts do not meet specified standards or documentation is missing, they may need to be replaced, causing cost and delay. Good purchasing decisions at the start reduce these risks.
Common problems with structural bolts and how to avoid them
Even with good products, several recurring issues appear on AU/NZ sites. Understanding them helps buyers ask the right questions.
Using non-conforming or mixed assemblies
Mixing bolts, nuts and washers from different sources or standards can lead to assemblies that look correct but do not meet AS/NZS 1252. For example, a nut with insufficient strength may strip before the bolt reaches design tension.
To avoid this, make sure orders clearly specify “complete assemblies to AS/NZS 1252” and that the supplier ships bolts, nuts and washers that are designed and tested together.
Over tightening or under tightening
If installers rely only on “feel” with powerful impact tools, bolt tension can vary widely. Excessive torque can damage threads or cause premature failure; too little torque can reduce preload and slip resistance. Training and clear tightening procedures are essential, as discussed in many steelwork guides. 设计手册
Galvanizing and friction factors
Hot dip galvanizing changes the friction between bearing surfaces. If the design assumes certain slip factors but the actual surface condition is different (for example, over-lubricated or not cleaned after galvanizing), slip-critical capacity may be lower than expected. Coordinating design assumptions, bolt assemblies and surface preparation procedures is key.
Storage and handling damage
Long sea journeys and rough handling can damage threads or coating. Proper packing – strong cartons, palletisation, and moisture protection – helps ensure that structural bolts arrive in good condition and ready for installation. Buyers can coordinate with suppliers to choose suitable packing options and small packs where needed, as described in Linkworld’s packing solutions. Jiaxing Linkworld Fastener
Procurement tips for overseas buyers supplying AU/NZ projects
When you are sourcing structural bolts from manufacturers overseas, good communication is as important as price. Here are some practical tips.
1. Specify the standards clearly
Instead of saying only “high tensile bolts”, define:
- AS/NZS 1252.1 assembly standard
- Property class (e.g. 8.8 or 10.9)
- Bolt type and dimensions (e.g. M20 × 80, hex head)
- Coating (e.g. hot dip galvanized, mechanical zinc)
- Any additional requirements (e.g. slip-critical joints, DTI washers, special markings)
Linkworld’s product catalogue for bolts, nuts and washers can be a useful reference when preparing your item list:
https://linkworldfast.com/product-category/bolts-nuts-washers/ Jiaxing Linkworld Fastener
2. Order assemblies, not individual parts
Make it clear that bolts, nuts and washers must be supplied as matching assemblies, packed and labelled together. This reduces the risk of mixing components from different batches or strength classes.
3. Ask about manufacturing process and QC
A supplier with its own cold forming and machining facilities, along with partner workshops, can control the full process from raw material to finished assembly. Linkworld, for example, focuses on cold-formed bolts and related components, supported by an in-house QC team and inspection equipment. Jiaxing Linkworld Fastener+1
When you request quotes, you can ask:
- How are bolt heads and threads formed?
- What inspection is done on each batch?
- Can they provide torque–tension test data or sample assemblies for your evaluation?
4. Coordinate packing and partial shipments
Many AU/NZ importers place one order but receive several shipments over the year. Working with a supplier who can hold stock and arrange multiple shipments can help you manage warehouse space while keeping consistent structural bolt quality and packing.
You can discuss options such as:
- Standard pallet patterns and carton sizes
- Small boxes for project kits versus bulk cartons for fabricators
- Special labelling for different construction categories or projects
For an overview of packing and product options, see:
https://linkworldfast.com/products/ Jiaxing Linkworld Fastener
5. Keep documentation organised
Before the bolts ship, make sure you receive:
- Mill certificates or material data (where required)
- AS/NZS 1252 assembly test reports
- Packing lists showing batch numbers, quantities and pallet IDs
Having these ready makes it easier to satisfy fabricators, inspectors and clients once the container lands.
How structural bolts connect to other components
Structural bolts rarely work alone. They interact with other components that you may also source from the same supplier.
Examples include:
- Stamped brackets, joist straps and braces – These need suitable hole sizes and thicknesses to work correctly with the selected bolt grade. See typical stamping parts here: https://linkworldfast.com/product-category/stamping-parts/ Jiaxing Linkworld Fastener+1
- Purlin and framing fasteners – Smaller structural screws and batten screws that tie the rest of the structure back to the main frame.
- Rigging items and safety hardware – Such as eye bolts or safety chains for lifting and restraint systems, which may be connected to structural steel bolted joints.
When you source these related items from one supplier, you can align dimensions, hole patterns and coatings so that the whole system works together.
Checklist for your next structural bolt inquiry
Before sending your next RFQ or purchase order for structural bolts, run through this checklist:
- Project location and environment
- Australia or New Zealand?
- Corrosion category (internal dry, industrial, coastal, marine)?
- Standards and design information
- AS/NZS 1252 assemblies required?
- Any reference to AS/NZS 5131 construction categories?
- Bolt details
- Size range and property class
- Coating and lubrication requirements
- Need for slip-critical joints and specific friction classes
- Assembly contents
- Bolt + nut + washer combinations
- Structural washers such as AS1252 types where required
- Testing and documentation
- What test reports and inspection documents are needed?
- Any project-specific requirements from the steel fabricator or client?
- Packing and delivery
- Bulk cartons, small boxes or kits?
- Pallet type and container loading plan
- Single shipment or multiple releases over time?
- Communication and drawings
- Do you have any connection details or sketches to share with the supplier?
- Are there special components (stamped plates, brackets, base plates) that should be sourced together with the bolts?
If you can answer these questions clearly, your discussions with the fastener manufacturer will be smoother and the final product is more likely to match site expectations.
Conclusion: treating structural bolts as part of the whole structure
Structural bolts in AU and NZ construction are more than big hex bolts. They are engineered assemblies governed by specific standards, used in carefully designed joints and subject to strict quality and inspection requirements. When you treat structural bolts as part of the entire steelwork system – from design codes to installation methods – you reduce risk and add value to your projects.
If you are planning a new project or reviewing your current structural bolt supply, you are welcome to discuss your list, drawings and packing needs with the Linkworld team. You can learn more about the company here:
https://linkworldfast.com/about-us/
To explore available products, including structural washers, hex bolts, stamping parts and other fasteners, visit:
https://linkworldfast.com/products/
For inquiries, BOMs or project discussions, please contact:
https://linkworldfast.com/contact/ or email info@linkworldfast.com. Jiaxing Linkworld Fastener+1
They can work with you to choose structural bolt assemblies and related components that meet AU/NZ standards and support safe, efficient construction on your projects.